[PATCH v11 16/46] KVM: guest_memfd: Return early if range already has requested attributes

[Ackerley Tng]

Provide a function to check that a range has given attributes.

Optimize setting memory attributes by returning early if all pages in the
requested range already have the requested attributes.

Reviewed-by: Fuad Tabba <tabba@xxxxxxxxxx>
Tested-by: Shivank Garg <shivankg@xxxxxxx>
Reviewed-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>
Reviewed-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
---
 virt/kvm/guest_memfd.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index d1134b23576e4..6dc199be0eb87 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -98,6 +98,24 @@ static bool kvm_gmem_is_shared_mem(struct inode *inode, pgoff_t index)
 	return !kvm_gmem_is_private_mem(inode, index);
 }
 
+static bool kvm_gmem_range_has_attributes(struct inode *inode,
+					  pgoff_t index, size_t nr_pages,
+					  u64 attributes)
+{
+	struct maple_tree *mt = &GMEM_I(inode)->attributes;
+	pgoff_t end = index + nr_pages - 1;
+	void *entry;
+
+	lockdep_assert(mt_lock_is_held(mt));
+
+	mt_for_each(mt, entry, index, end) {
+		if (kvm_gmem_get_attributes(inode, entry) != attributes)
+			return false;
+	}
+
+	return true;
+}
+
 /*
  * Returns a locked folio on success.  The caller is responsible for
  * setting the up-to-date flag before the memory is mapped into the guest.
@@ -623,12 +641,15 @@ static int __kvm_gmem_set_attributes(struct inode *inode, pgoff_t start,
 	pgoff_t end = start + nr_pages;
 	struct maple_tree *mt;
 	struct ma_state mas;
-	int r;
+	int r = 0;
 
 	mt = &gi->attributes;
 
 	filemap_invalidate_lock(mapping);
 
+	if (kvm_gmem_range_has_attributes(inode, start, nr_pages, attrs))
+		goto out;
+
 	mas_init(&mas, mt, start);
 	r = kvm_gmem_mas_preallocate(&mas, attrs, start, nr_pages);
 	if (r) {

-- 
2.55.0.887.g758fc8c411-goog